1. Technical Field
The present invention relates generally to chemical energy conversion engines, and specifically, to methods and apparatus for recovering mechanical energy for gaseous fuel chemical energy conversion engines.
2. Background
Liquid gasoline is the most commonly used fuel source for internal combustion engines for automotive vehicles. Liquid gasoline has a high volumetric density of energy and therefore may be easily transported. Gasoline, however, is formed from fossil fuels and therefore the resources are limited.
Automakers are increasingly investigating alternative sources for powering vehicles such as propane, natural gas, and hydrogen fueled chemical energy conversion engines. Examples of chemical energy conversion engines are not limited to but include internal combustion engines, gas turbine engines, and chemical fuel cells. These vehicle systems require highly pressurized gases or liquids that must be stored on-board a vehicle. The fuel contains stored mechanical potential energy, due to the elevated pressure, in addition to chemical potential energy. Typically, during operation of the vehicle a pressure regulator reduces the high-pressure fuel to a lower level for use within the vehicle engine. Mechanical energy is lost to the environment when expanding through a pressure regulator. Because the volumetric energy density of gaseous fuel is substantially lower than gasoline, highly compressed fuel is often used to achieve vehicle range levels desired in current automotive vehicles.
Therefore, it would be desirable to further increase the useful energy of a compressed fuel source to increase the overall efficiency of the system.
The present invention increases the total work output of a chemical energy conversion engine system for an automotive vehicle. The present invention uses a compressed fuel source having a first fuel pressure. An expansion device is coupled to the compressed gaseous fuel source and reduces the first pressure to a second pressure lower than the first pressure. The expansion device generates a first quantity of work and forms a reduced pressure gaseous fuel. A chemical energy conversion engine is coupled to the expansion device and receives a reduced pressure fuel. The chemical energy conversion engine generates a second quantity of work in response to the decompressed fuel.
In a further aspect of the invention, the first quantity of work and the second quantity of work may be coupled to an output shaft such as the crankshaft of an internal combustion engine. In another aspect of the invention, the first quantity of work may be coupled to an accessory either directly or indirectly. Indirect coupling may, for example, be performed using an accessory drive belt of an engine, or using a generator to produce electricity.
In a further aspect of the invention, a method of operating a compressed fuel chemical energy conversion engine comprises:
expanding a compressed gaseous fuel in an expansion device to form a reduced pressure gaseous fuel;
generating a supplemental work output from the expansion device;
operating a chemical energy conversion engine with the decompressed fuel to generate primary work; and
coupling the supplemental work output to a vehicle component.
One advantage of the invention is that the efficiency of a compressed fuel system is increased. Another advantage of the invention is that a heat exchanger may be added to re-route waste heat from the chemical energy conversion engine to the compressed gaseous fuel to further increase the system efficiency.
Other advantages and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.